1. Field of the Invention
The present invention in general relates to fluid detectors and more particularly to such detectors that can differentiate between the presence of hydrocarbons, water, and the dry condition.
2. Description of the Prior Art
The contamination of ground water by hydrocarbon leaking from underground tanks has become a serious problem in recent years, particularly since tanks installed during a gasoline station boom that occurred many years ago are now becoming aged and increasingly subject to leaks. When an underground hydrocarbon storage tank leaks, not only is groundwater contaminated but the party responsible must often pay substantial costs for clean-up. Thus it is essential that leaks be detected as soon as possible. For these reasons, leak detectors that can monitor the environment in the vicinity of a tank and can differentiate between hydrocarbon, water and the dry condition and provide an alarm on the detection of hydrocarbon have been developed. See, for example, U.S. Pat. No. 4,586,033 issued to Raymond J. Andrejasich. Other such detectors have provided a programmable relay which can be set to be activated upon any combination of dry, hydrocarbon, or water. See U.S. Pat. No. 4,644,354 issued to Roy E. Kidd. This flexibility is useful because sensing probes may be placed outside a tank, where they normally encounter water and thus it is desirable to alarm only in response to hydrocarbon, or between the inner and outer tanks of a double-walled tank where they are normally dry and thus it is desirable to alarm on either hydrocarbon or water. In all of the above systems, the audible alarm provided is the same for any condition for which it is programmed to be activated.